There was a push a couple years back to collect that data. Mozilla Test Pilot. They kept track of how long people kept browsers open, how many tabs they had and how they were used, opened, closed... All of this was anonymized and collected in all sorts of pretty graphs.

The site seems down, now, but that data was taken and helped shape the changes we're seeing now.

Old link: https://testpilot.mozillalabs.com/testcases/tab-open-close/a...

I leave my browser open always, only closing it to clear out the memory leaks. So start-up isn't terribly important to me.

My FF opens pretty quickly by my standards. What seems to take forever is closing it. It seems to me that there ought to be some performance optimizations to be found in that area.

Are you using Readability? There was a recent change made to fix massive shutdown hangs when using that addon (or others that use FUEL):

https://hg.mozilla.org/mozilla-central/rev/139e8e845aa5

Anecdotally I close my browser 5-10 times a day. It opens immediately so there's no reason to keep it open if you're done with your tasks. And having fewer programs open makes it easier for me to focus on my task at hand.

I've seen that my battery life suffers when I have too many programs running that I don't currently use, so I make it a habit to close a program when I notice I haven't used it, or know I won't be for a few minutes.